The present invention relates to a silicone rubber composition or, more particularly, to a silicone rubber composition having excellent workability in processing and moldability by extrusion so as to be useful as a material of rubber rollers and the like as well as to a method for the preparation of such a silicone rubber composition.
Silicone rubbers are widely used in various fields of industrial applications as a material of electric and electronic parts, buildings, automobile parts, instruments for office automation and the like by virtue of the excellent characteristics of the shaped and cured silicone rubber articles such as heat resistance, cold resistance, weatherability, durability, mold-releasability, electric properties and so on. One of the most rapidly growing application fields of silicone rubbers in recent years is as a material used in office-automation instruments such as rubber rollers in electrophotographic copying machines, printers in word processors and the like along with the remarkable progress of office automation so that consumption of silicone rubbers as a material of rubber rollers is expanding at a great rate year by year. As is well known, the basic ingredients in silicone rubber compositions are an organopolysiloxane having gum-like consistency and a finely divided silica filler for reinforcement while the mechanical properties of cured silicone rubber articles can be improved by increasing the amount of the reinforcing silica filler compounded with the organopolysiloxane gum.
However, it is generally a difficult matter to prepare a silicone rubber composition compounded with a reinforcing silica filler in an amount as large as desirable due to the limited compatibility between the silica filler and the organopolysiloxane gum. Accordingly, an established practice therefor is that a silicone rubber composition is admixed with a so-called wetting agent or compatibility improver for the reinforcing silica filler, which is typically a low molecular weight organopolysiloxane having silanolic hydroxy groups at the molecular chain ends, diphenylsilane diol, alkoxysilanes and the like, in order that an increased amount of the reinforcing silica filler can be compounded with the organopolysiloxane gum. Needless to say, the amount of the wetting agent must be increased more and more when the amount of the reinforcing silica filler to be compounded with the organopolysiloxane gum is desired to be larger and larger. A disadvantage is unavoidable, however, when the amount of the wetting agent is increased that the silicone rubber composition is imparted with a decreased plasticity to exhibit stickiness on the surface resulting in poor workability of the composition in roll-milling or extrusion molding not to be suitable as a material of silicone rubber rollers.